The present invention relates to an apparatus and method for the gray scale display of a liquid crystal display device, and more particularly, to an apparatus and method for multi-level gray scale display which provides a cost reduction effect by using an amplitude modulation method without an analog driving integrated circuit.
Well-known addressing methods used in liquid crystal display devices include the APT, IAPT, BAT, HAT, IHAT, AAT and SAT methods, and methods for displaying the gray scale include FRC, PWM, PHM, AM and dithering. Among these conventional gray-scale display methods, the frame conversion (FRC) method generates flicker in fast response LCDs. In the case of the amplitude modulation (AM) method or pulse height modulation (PHM) method which is used in the active addressing technique (AAT), there is a problem of a remarkable increase in the number of voltage levels applied at column electrodes as the number of levels of gray scale is increased. Since it is difficult for the voltage level to be exactly controlled due to the increased of number of voltage levels, an analog driving integrated circuit (IC) has generally been used.
FIG. 1 is a schematic diagram showing the construction of a conventional analog driving IC. The analog driving IC shown in FIG. 1 comprises a sampling pulse generator 70, a sampling holder 80, and an output buffer 90. Sampling pulse generator 70 comprises a logic circuit 72 for receiving a control signal via terminal 100 and a shift clock signal to generate the sampling pulse and a level converter 74 for level-converting the output of logic circuit 72, thereby generating a plurality of sampling pulses. In sampling holder 80, the video signal is input to an analog switching portion 82 via terminal 101, is switched according to the sampling pulse and temporarily stacked in a sampling condenser CSPL. The accumulated signal is output according to an output enable signal input to an analog switching portion 86 via terminal 107, is held by a hold condenser CH and is output to the column electrodes of the liquid crystal panel via output buffer 90.
If the analog driving IC as described above is used in the case of many gray scale displays, the cost of it is largely due to the high level of the column voltage, thereby raising the cost for manufacturing.